The present invention relates to a urethane curable composition containing a catalyst, polyol, polyisocyanate, and silica particles.
Commodity plastics such as acrylic resins, polycarbonate resins, polystyrene resins, and ABS resins are used in various fields because plastic molding is easily performed and they are light-weight and are superior in impact resistance. However, molded articles formed of these resins have, for example, poor scratch resistance and wear resistance on surfaces thereof as compared to glass and the like, and thus the appearance and functions thereof are likely to deteriorate when scratched by a nail or when damaged or depressed due to contact or impact of dust, pebbles, and the like. In order to solve these problems, a method of coating a surface of a resin molded article with a coating film having superior scratch resistance to protect the surface is generally used, and various curable compositions having such a function have been proposed. Among these, curable compositions using a urethanization reaction between polyol and polyisocyanate are suitable for thermal curing at a low temperature at which a resin molded article is not thermally deformed and for short-time curing, and various compositions have been proposed.
Among these urethane curable compositions, coating films containing a urethane curable composition and silica particles have high surface hardness and are superior in scratch resistance, and thus various compositions have been proposed (for example, Japanese Unexamined Patent Publication Application No. 2002-327146, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-539603, Japanese Unexamined Patent Publication Application No. 2010-189477, and Japanese Unexamined Patent Publication Application No. 2012-21111).
On the other hand, examples of a catalyst of a urethanization reaction between a hydroxyl group and isocyanate include metal compounds such as dibutyltin dilaurate, tin octylate, and lead naphthenate and salts thereof (F. Hostettler, E. F. Cox, Ind. Eng. Chem., 52, 609 (1960)); metal chelate compounds such as zirconium tetra acetylacetonate and titanium diisopropoxy bis(ethyl acetoacetate); and organic amines such as triethylenediamine, triethylamine, and tri-n-butylamine (J. Burkus, J. Org. Chem., 26, 779 (1961)) and salts thereof (Japanese Unexamined Patent Publication Application No. 60-240415). Among these, in particular, a dialkyltin compound such as dibutyltin dilaurate is generally widely used due to its high catalytic activity performance.
However, an acidic material such as silica particles having the same chemical structure as that of silica gel is known as a catalyst deactivating agent of a urethanization reaction between a hydroxyl group and an isocyanate group or an isocyanurating reaction between isocyanate groups (Japanese Unexamined Patent Publication Application No. 08-027123). In a urethane curable composition containing such an acidic material, it is difficult to make a curing reaction progress sufficiently. Accordingly, there has been a need for an improved urethane curable composition.